Assistive Robotic Devices for Dynamic Locomotion

This full day workshop at Robotics Science and Systems (RSS) 2016 will provide a comprehensive discussion of active lower-limb prosthetics and lower-limb exoskeletons that goes beyond simple questions of mechatronic design and controller implementation. It will address electromechanical design, control strategies, emulation, optimization, and clinical assessment. The workshop features an open call for poster submissions. Additionally, it will include a round table discussion between participants and end users of this technology.

   

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Overview

RSS Workshop: Assistive Robotic Devices for Dynamic Locomotion

Full Day - Sunday June 19th, 2016 in 2245 North Quad

University of Michigan, Ann Arbor, MI

Assistive robotic devices constitute a growing area of robotics research. These systems have the potential to improve mobility for millions of people, both healthy and disabled. The goal of this full day workshop is to provide a comprehensive discussion of active lower-limb prosthetics and lower-limb exoskeletons that goes beyond simple questions of mechatronic design and controller implementation. In particular, the workshop is targeted at devices that are capable of dynamic locomotion as they replace and /or enhance functionality. For these kinds of systems, the interaction between user and assistive robotic device is of particular importance. Among other topics, we will address electromechanical design, control strategies, emulation, optimization, and clinical assessment.

Confirmed speakers include a mix of senior and junior figures from the robotics and biomechanics communities, and the workshop features an open call for poster submissions. Interaction between participants will be fostered by moderator-led discussions after each talk, informal interaction during extended break periods, a poster session, and an informal social event at the conclusion of the workshop. Discussions will be aimed at contrasting prevailing approaches and identifying areas for future research. Additionally, the workshop will include a round table discussion between participants and end users of this technology. This discussion will help researchers develop an improved understanding of patient interest in specific design features. Students, early-stage researchers, and established roboticists with a growing interest in active prosthetics are especially encouraged to attend.

Please see the website for RSS 2016 for additional information. In the future, this site will also provide information on conference registration, travel, lodging, and other logistics.

Call for Contributions

We are now accepting submissions for poster presentations at the workshop “Assistive Robotic Devices for Dynamic Locomotion”. Submissions should be targeted at the topics outlined in the workshop description presented above. In order to spark rich and fruitful discussions among attendees, we strongly encourage the submission of ideas and projects that focus on concepts emerging technologies and that may still be in their developmental stages. With this in mind, we will give attendees a choice of whether their abstract will be made publicly available on the conference webpage or not.

Submissions are limited to a maximum of two pages and should adhere to the formatting guidelines outlined in the following formatting templates (LaTeX or Word). All submissions should be emailed as a PDF to AssistiveRoboticDevicesRSS@umich.edu.

Important Dates
Submission Deadline: April 29, 2016
Acceptance Notification: May 13,2016
Workshop Date: June 19, 2016

Program

8:30	Welcome
8:40 - 10:00	Talks and Discussion
8:40	Tommaso Lenzi - Exoprosthetics
9:00	Gregory Sawicki - Biologically Inspired Design
9:20	Robert Gregg - Phase-Based Control
9:40	Peter Adamczyk - Semi-Active Devices
10:00 - 10:30	Coffee Break
10:30 - 11:10	Talks and Discussion
10:30	Heike Vallery - Lower-Extremity Prosthetics
10:50	Hartmut Geyer - Local Reflexive Control
11:10 - 12:30	Poster Session
12:30 - 1:50	Lunch Break
1:50 - 3:10	Talks and Discussion
1:50	Elliott Rouse - Impedance-Inspired Design
2:10	Deanna Gates - Assessment of Clinical Value
2:30 - 3:30	Focus Group Round Table Discussion
3:30 - 4:00	Coffee Break
4:00 - 5:30	Talks and Discussion
4:00	Nicholas Fey - Task-Control Interactions
4:20	David Remy - Body-in-the-Loop Optimization
4:40	Jason Wilken - Assessment of Clinical Value
5:00	Brian Lawson - Alternative Applications: Cycling
5:30 - Late	Informal Social Event at Arbor Brewing Company Brew Pub

List of Confirmed Speakers with Tentative Topics, Titles, and Abstracts

Focus Group Round Table Discussion
Description: The workshop will include a round table discussion between participants and several end users of robotic technology (prostheses and exoskeletons). The goal of this discussion will be to identify the limitations of current technology, specific needs of the users, and barriers to acceptance of new technology.

Peter Adamczyk Assistant Professor of Mechanical Engineering, University of Wisconsin, Madison
Topic: Semi-active devices
Title: Semi-active foot prostheses for low-power gait restoration
Abstract: A common biomimetic approach to active lower limb prostheses is to add control to the prosthetic ankle, injecting power to push-off and adjusting angle for different terrain. Yet, artificial limbs offer an opportunity to improve function in novel, nonbiomimetic ways as well. One such approach is through modulation of prosthesis mechanical properties, without the addition of power. This approach aims to improve gait by exploiting biomechanical workarounds for lost function, rather than directly replacing it. This presentation discusses such "semi-active" devices and the concepts underlying their biomechanical function.

Nicholas Fey Assistant Professor, Bioengineering, Mechanical Engineering, University of Texas at Dallas
Topic: Interactions between task and motor control
Title: Intrinsic device sensing to assist ambulation and weight transfers of transfemoral amputees
Abstract: Lower-limb amputees commonly experience abnormal gait characteristics and chronic pain. These behaviors restrict mobility and are attributed to the use of prostheses that inadequately restore muscular functions. Currently, the field of rehabilitation engineering is met with important questions such as how biologically-inspired should assistive devices be and in what tasks are active systems needed. I will present recent efforts at providing above-knee, transfemoral amputees with control of an active knee and ankle prosthesis. Effective strategies are needed to increase the viability of such devices for use during common activities of daily living. I will present basic approaches that aim to improve generalizability of control by allowing user regulation of power delivery during ambulation and weight transfer movements. Tasks that tend to both increase and decrease the mechanical load on the device will be examined. The common factor linking the control approaches of these different tasks is the use of intrinsic sensing located onboard the device to modulate the simultaneous delivery of knee and ankle power based on user input. These approaches will be evaluated with respect to user training as well as evidence of improved biomechanical benefits.

Deanna Gates Assistant Professor, School of Kinesiology, University of Michigan
Topic: Assessment of clinical value
Title: Why don’t powered prostheses work for everyone?
Abstract: Powered prostheses have promise to restore the function that has been lost with the loss of the musculature. However, the benefits of these devices are mixed. This talk will focus on how the characteristics of the individual can influence the success of the device. Specifically we explore the success of a powered ankle prosthesis in populations of different ages, with different cardiac fitness levels, muscle strength, and ability to coordinate their movements. We have also explored how successfully users have adapted to robotic devices in order to reduce the demands on their residual musculature. Somewhat surprisingly, those who are most successful are not those with the most to gain, but those who already have sufficient strength to actively adjust to whatever actuation the ankle provides.

Hartmut Geyer Assistant Professor, Robotics Institute, Carnegie Mellon University
Topic: Local reflexive control
Title: Toward balance recovery with active leg prostheses using neuromuscular model control
Abstract: With the advent of active artificial limbs, the stability and robustness of amputee gait becomes an increasingly active research area. This is a timely development. Lower limb amputees remain at high risk of falling as current prosthetic legs provide only limited functionality for recovering balance after unexpected disturbances. To improve balance recovery in amputee gait, we explore human-inspired limb controls for active leg prostheses. These controls consider the global leg function in locomotion and are based on a neuromuscular model of human gait. In simulation, we show that the proposed prosthesis control leads to robust amputee walking in the presence of unexpected ground changes, trips, and pushes to the body. In initial hardware experiments with one non-amputee user focusing on swing leg tripping, we find that the control effectively handles disturbances in early and late swing, but fails to avert falls for mid-swing disturbances. We present our current efforts to overcoming this limitation and to testing the control with amputees.

Robert Gregg Assistant Professor, Bioengineering, Mechanical Engineering, University of Texas at Dallas
Topic: Phase-based control
Title: Towards unified control of prosthetic legs with a human-inspired phase variable
Abstract: The gait cycle is typically viewed as a periodic sequence of discrete events, starting with heel contact during initial stance and ending with knee extension during late swing. This convention has informed the design of control strategies for powered prosthetic legs, which almost universally switch between several distinct controllers throughout the gait cycle. However, this methodology is not necessarily robust to perturbations that push the gait cycle forward or backwards, preventing active prostheses from responding in harmony with the human user. Instead of discretely representing the phases of gait, a continuous representation could parameterize a nonlinear controller for larger portions, or the entirety, of the gait cycle. In particular, the concept of a mechanical phase variable has been widely successful in controlling the progression of leg joints in dynamic walking robots. However, it is unclear what phase variables, if any, can robustly represent the phase of human locomotion. This talk will share a recent perturbation study with 10 able-bodied human subjects, observing a mechanical variable that robustly parameterizes leg joint patterns over the entire gait cycle (with correlation coefficients between 0.95 and 0.997). A unifying prosthetic leg controller is then designed around this phase variable to synchronize prosthetic joint patterns with the location of the human body. The viability of this approach is demonstrated by experiments with human subjects walking on a powered knee-ankle prosthesis at variable speeds.

Brian Lawson Post-Doctoral Scholar, Center for Intelligent Mechatronics, Vanderbilt University
Topic: Alternative applications: cycling
Title: Identifying and Supplementing User Effort in Transfemoral Amputee Cycling
Abstract: Some of the difficulties that arise in controlling a powered prosthesis for gait can be avoided in simpler applications such as cycling. The differences between these two activities with respect to the control problem will be discussed, and a methodology for providing supplemental knee torque in a powered transfemoral prosthesis will be presented. Finally, the results of several experiments with an amputee subject will show improvements in torque symmetry and a reduction of the metabolic burden using this controller.

Tommaso Lenzi Research Scientist, Center for Bionic Medicine, Rehabilitation Institute of Chicago
Topic: Exoprosthetics
Title: Powered exoprostheses for individuals with transfemoral amputation
Abstract: Powered prostheses face an inherent paradox: in pursuit of decreased user effort they add weight—in the terms of motors, transmission systems, and batteries—that ultimately require more effort from the user due to the location of the components. Thus the field has been focusing on better actuators and better control algorithms, but can hardly succeed due to raw physics. However, phrasing the question this way has also suggested an innovative way in which to solve it. It is possible, by actuating different parts of the body, to achieve the same energy generation but without the mass-cost required of the user. This can most easily be accomplished by fusing an exoskeleton together with a prosthesis. Rather than restoring the energy generation ability of the missing limb, an exoprostheses aims at augmenting the strength of the residual limb with an assistive energy. As assisting the residual limb requires lower torque than restoring physiological energy at the missing joints, an exoprosthesis can be made lighter than an active prosthesis. In addition, the exoprosthesis actuation system is located close to the body center of mass, thus minimizing the user cost of carrying additional mass. The key innovativeness of the exo rosthesis approach is therefore in pursuing asymmetric joint energetics. Our hypothesis is that amputee users can recover physiological ambulation effort with a non-physiological joint biomechanics—e.g., larger positive energy generation at the hip joint rather than ankle—when robotic assistance is provided at the residual limb. This talk will discuss the scientific and technological challenges behind the exoprosthesis approach, focusing on ambulation biomechanics, mechatronic design, and robotic control. Furthermore, I will present experimental results showing that transfemoral amputee subjects using their prescribed passive prostheses reduced metabolic energy consumption in walking when assisted by an autonomous hip exoskeleton.

C. David Remy Assistant Professor of Mechanical Engineering, University of Michigan
Topic: Body-in-the-loop optimization
Title: Body-in-the-loop optimization of assistive robotic devices
Abstract: In our research, we investigate the potential of conducting online optimizations of assistive robotic devices. To this end, we estimate a physiological value function from sensor data while a user is wearing the device. This estimate is used in real-time in an optimization algorithm to inform the iterative search for optimal parameter values of a controller. Among potential applications for this methodology is the control of powered robotic prostheses, orthoses, or exoskeletons. This presentation will focus on the evaluation of our proposed method in a toy-problem: the optimization of step frequency during treadmill walking. To evaluate the methods in a simple and repeatable way, we prescribed step frequency via a metronome and optimized this frequency to minimize metabolic energetic cost. We compare three algorithms (Steady-State Cost Mapping, Instantaneous Cost Mapping, and Instantaneous Cost Gradient Search). Steady-State Cost Mapping is an established technique that fits a cubic polynomial to averages of steady-state measures at different parameter settings. The optimal parameter value is determined from the polynomial fit. Using a continuous sweep over a range of parameters and taking into account measurement dynamics, Instantaneous Cost Mapping identifies a cubic polynomial more quickly. Instantaneous Cost Gradient Search uses a similar technique to iteratively approach the optimal parameter value using estimates of the local gradient.

Elliott Rouse Assistant Professor, Physical Medicine and Rehabilitation, Mechanical Engineering, Biomedical Engineering, Northwestern University
Topic: Impedance-inspired design
Title: Joint impedance modulation and the relevance to the design and control of robotic prosthetic technologies
Abstract: To date, many wearable robotic technologies have struggled to provide the assistance benefit we had hoped for these exciting devices. Despite much encouraging work, robotic prosthetic legs have yet to improve the metabolic cost of above knee amputees. In this talk, I will discuss one potential solution to this challenge. I propose to identify and incorporate the modulation of joint mechanical impedance during locomotion into the design and control of wearable robots. The identification of ankle impedance during the stance phase of walking was recently completed, and I will discuss how these data are currently being used to develop novel prosthetic technologies. I will underscore this work with single-joint studies that investigate the role of joint impedance during leg movements, including how these properties are related to the quasi-stiffness during movement, a metric often used to design passive prostheses. Through incorporating joint mechanics during locomotion into the design and control of wearable assistive technologies, we can hopefully match all the features of an intact neuromuscular system: joint kinetics, kinematics and mechanical impedance, thereby improving the quality of life for individuals with amputations.

Gregory Sawicki Associate Professor Biomedical Engineering, North Carolina State University and University of North Carolina at Chapel Hill
Topic: Biologically inspired design
Title: A biologically inspired approach to lower-limb exoskeleton design
Abstract: The goal of the Human Physiology of Wearable Robotics (PoWeR) Laboratory is to discover and exploit key principles of locomotion neuromechanics in order to build wearable devices that can augment intact and/or restore impaired human locomotion. The primary performance goal of such devices is to reduce metabolic energy consumption of the user. Our design approach is motivated by two key mechanisms observed in human gait that are crucial to efficient movement. The first is optimally timed, impulsive ankle joint push-off for propelling the body forward. The second is the effective cycling of mechanical energy from the body's center of mass to elastic tissues (i.e. tendon and aponeurosis) and back. In the first part of the talk I will highlight our recent work using an in-lab, pneumatically powered ankle exoskeleton with a novel neuromechanics based controller to help stroke survivors regain symmetric push-off mechanics. Then, I will discuss the motivation and basic science behind the design of a portable, passive elastic exoskeleton and novel clutching mechanism that can provide a spring in your step by storage and release of elastic energy in a parallel elastic element worn about the ankle (i.e. exo-tendon) during human walking. We recently demonstrated that this device can reduce the metabolic cost of normal walking by ~7% below normal without adding any external energy from batteries or motors. We contend that simple, bio-inspired designs promise more functionality than current passive AFO product lines; and a cheaper, more practical alternative to fully powered lower-limb exoskeletons now coming to market.

Heike Vallery Associate Professor of Mechanical Engineering, Delft University of Technology
Topic: Lower-extremity prosthetics
Title: Unexpected observations with lower-extremity prostheses
Abstract: Today, sophisticated robotic leg prostheses are emerging, aiming to rival biological function. For example, we have recently introduced ANGELAA, an active knee designed to replicate physiological impedance modulation during gait. In experiments, we showed that such a device can restore near-physiological gait. However, we have also observed several unexpected outcomes, particularly in terms of discrepancies between model predictions and user preferences regarding impedance settings. A similar effect occured when we investigated sensory substitution concepts to augment the user's sense of balance, where we observed that user perception and "objective" evaluation of performance were not aligned. With the aim to spark a discussion, this talk will highlight some main concepts and experiences gained, and motivate new directions. It will end with an outlook on our most recent developments in the domain of active leg prostheses.

Jason Wilken, PhD Director, Military Performance Lab, Center for the Intrepid, U.S. Army
Topic: Assessment of clinical value
Title: What are we really trying to accomplish? Value and device development
Abstract: Assistive technologies can be developed to restore, replace or augment function in limbs affected by injury or disease processes. Although many types of robust and technologically sophisticated robotic systems have been developed, few make it out of the lab and into widespread use. Reasons include clinical feasibility, reimbursement, lack of evidence demonstrating benefit and/or patient satisfaction. This talk will address the systematic assessment of novel technologies in clinical and laboratory settings and the concept of clinical value as it relates to future application of advanced technology.

List of Confirmed Poster Presentations

Scott Brandon - Measurement System for Gait Mechanics during Exoskeleton Use
Jeffrey Koller - "Body-in-the-Loop" Optimization of Pneumatically Powered Bilateral Ankle Exoskeletons
Kimberly Ingraham - Influence of Uncertainty in Metabolic Dynamic Time Constant on Instantaneous Cost Mapping Techniques
Richard Nuckols - Evaluating Exoskeleton Assistance at Variable Gait Speeds Using Traditional and Instantaneous Measures of Metabolic Cost
Hongliang Ren - A Preliminary Study of Force Estimation Based on Surface EMG: Towards Neuromechanically Guided Soft Oral Rehabilitation Robot
John Spanias - Preliminary Results for an Adaptive Pattern Recognition System for Novel Users Using a Powered Lower Limb Prosthesis
Max Sheppard - Torque-Controllable Knee Exoskeleton for Stroke Mobility Assistance
Deema Totah - EMG-based Prediction of Lifted Loads for Assistive Device Applications
Philip Vu - Extracting Neuroprosthetic Control Signals from Regenerative Peripheral Nerve Interfaces in Human Subjects

Organizers

C. David Remy, Department of Mechanical Engineering, University of Michigan
Deanna Gates, School of Kinesiology, University of Michigan
Steve Collins, Robotics Institute, Carnegie Mellon University